Within a process chamber of a semiconductor processing system, a substrate is typically supported by a substrate support while being processed. In many such systems, the substrate support is heated to raise the temperature of the substrate during one or more of the process steps. The heater is generally a coil of resistive wire or a metalized layer. When current is applied to this wire or layer, the heater generates heat that is conductively transferred through the substrate support to the substrate.
In some cases, a single zone heater is used to heat a substrate. The disadvantage of using a single zone-heater is that the center of a single zone heater is typically hotter than the outer edges of the single zone heater, which can result in non-uniform deposition of material onto the substrate. A multi-zone heater can provide more uniform heat to a substrate. However, a disadvantage of a multi-zone heater is that the temperature of a multi-zone heater, and thus the amount of heat transferred to the substrate is difficult to measure and control. For example, one approach used to determine the temperature of an outer zone of a multizone heater is to monitor an amount of power being delivered to an inner zone of the heater, to multiply the power by an experimentally calculated power ratio, and then to apply that power to the outer zone. However, the accuracy of this methodology is affected by varying process conditions within the process chamber of a semiconductor processing system.
Thus, the inventors have provided improved methods and apparatus for controlling the temperature of multi-zone heater in a process chamber.